This invention relates to a telecommunication switch to be used in public switching telephony networks, comprising a plurality of Synchronous Digital Hierarchy (SDH) hardware interfaces, each comprising-working link connecting means, being designed to be connected to a working SDH link and protection link connecting means, being designed to be connected to a protection SDH link associated to the working SDH link of the SDH hardware interface, wherein to each of said SDH hardware interfaces a SDH termination module is connected and an operating method for handling SDH signals transmitted by a protection SDH link associated to a working SDH link of a SDH hardware interface of a telecommunication switch according to the invention.
SDH is an international digital telecommunications network hierarchy which standardises transmission around the bit rate of 51.84 megabits per second, which is also called STS-1. Multiples of this bit rate comprise higher bit rate streams. Thus STS-3 is 3 times STS-1, STS-12 is 12 times STS-1, and so on. STS-3 is the lowest bit rate expected to carry ATM traffic, and is also referred to as Synchronous Transport Module-Level 1 (STM-1).
A working SDH link (primary link) is defined as a default link for transferring data (working SDH signals) to be switched by the telecommunication switch. A protection link (secondary link) is defined as a link for transferring the data (protection SDH signals) to be switched by the telecommunication switch in case of a failure occurring on the primary link. Primary and secondary link may be implemented as an electrical and/or an optical data transmission connection. A telecommunication switch is equipped with means for switching (protection switching) data received from the primary and the secondary link to spare hardware elements in case of failure of a hardware element, e.g. a SDH hardware interface (applique) and/or a SDH termination module, used for switching the data. These means are called Equipment Protection Switching (EPS) means or equipment protection arrangement. An applique is used for switching data transmitted by SDH links according to a destination of the data. According to known physical reasons each SDH link has to be connected to a SDH termination module. Therefore a SDH termination module is connected to each applique.
According to the state of the art, a separate equipment protection switch, using extra space in a rack, wherein the hardware modules of a telecommunication switch are positioned, is used to switch SDH links, meaning working and/or protection link, from an active to a spare termination equipment. Each equipment protection switch is associated to a group (protection group) of a number N of SDH hardware interfaces and SDH termination modules. Different solutions are used for equipment protection switching, depending on whether electrical or optical transmission connections are used.
Separate equipment protection switches for optical and electrical SDH links are used. Therefore several slot positions in a rack per protection group (space) for a dedicated equipment protection switch are needed. Furthermore, the effort for hardware elements to be used for protection switching is high.